The invention relates to compound semiconductor structures provided with lattice and polarity matched heteroepitaxial layers.
There has been a major international effort on the heteroepitaxial growth of compound tetrahedrally coordinated semiconductors on Si substrates by MBE, MOCVD, etc.; on the fabrication of devices and circuits in these layers; and on the monolithic integration of such components with Si circuits fabricated on the same wafer. This effort is based on the significant potential that epitaxial growth of dissimilar semiconductor structures holds for technological applications. Nevertheless, relatively little theoretical work has been performed to understand the fundamental interactions and global issues governing the initial stages of growth and the structure of the first few mono-layers in these systems.
Of specific interest, for example, are the prototypical optically active systems GaAs on Si(100) and GaN on SiC/Si. At present, optoelectronics involves growth of structures like GaAs (an optical material because of its direct band-gap) on substrates of Si (an electronic material with an indirect band-gap). For the future, GaN is of particular interest for optoelectronics applications in the blue and near UV because of its direct wide band gaps. Unfortunately, the large lattice constant mismatches between the substrates and the epitaxial layers cause many defects to be created and propagate from the interface, as can be seen in Table 1 provided hereinafter. Moreover, this is exacerbated by the interface charge mismatch caused by polarity differences between GaAs and Si.
Table 1 illustrates the typical structures used in the electronics industry and their experimental lattice constant mismatches relative to Si Δa/aSi. Most of the structures have a large lattice constant mismatch with Si. For those with a small lattice constant mismatch, there is still the problem of polarity mismatch.
TABLE 1CompoundΔa/aSi{%}PolarSi0noGe+4.16noCuCl−0.46yesZnS−0.41yesGaP+0.37yesAlAs+3.48yesGaAs+4.11yesZnSe+4.36yesInP+8.06yesInAs+11.14yes
Therefore, there is a need for a semiconductor structure with epitaxial layers that are polarity and lattice matched, and which exhibit tunable properties to obtain, for example, a direct band gap.